This invention relates generally to bicycles, and in particular to two-wheel-drive bicycles.
Bicycles have traditionally operated as a single-wheel-drive vehicle. As is evidenced by their popularity, single-wheel-drive bicycles are suitable in most cases. Because they only employ single-wheel drive, however, the use of bicycles are, for the most part, somewhat limited to prepared surfaces such as paved streets, sidewalks, and groomed paths. Although just about everyone who has ever ridden a bicycle has ridden on gravel or unprepared surfaces, all riders know that it is more difficult to ride on these types of surfaces due to the fact that drive is being generated by only the rear wheel.
In any event, single-wheel-drive bicycles are the norm because of difficulties involved in transferring to the front wheel the drive generated by the rider. The difficulty in generating drive via the front wheel of a bicycle results from the need to allow the fork (on which the front wheel is mounted) freedom to turn substantially in either direction from the center position in order to permit the cyclist to steer the bicycle. Because the fork must be free to turn, it is not possible to directly connect the pedals to the front wheel.
While two-wheel-drive bicycles have been proposed, there remains a need for an easily-operable and readily steerable two-wheel-drive bicycle, so that riders will have greater opportunity for enjoyable cycling on off-road trails and other unprepared surfaces. Therefore, a two-wheel-drive bicycle overcoming various problems and shortcomings of the prior art would be an important improvement in the art.
An object of the invention is to provide a two-wheel-drive bicycle that overcomes some of the problems and shortcomings of the prior art.
Another object of the invention is to provide a two-wheel-drive bicycle that allows the fork assembly to freely turn in order to steer the bicycle.
Still another object of the invention is to provide a bicycle that includes a gear arrangement that allows both wheels to act as drive wheels.
Yet another object of the invention is to provide a two-wheel-drive bicycle that can be converted to a single-wheel-drive bicycle.
How these and other objects are accomplished will become apparent from the following descriptions and from the drawings.
The invention involves an improvement to a two-wheel-drive bicycle that includes: (1) a frame having front and rear portions and a center portion with upper and lower ends; (2) a fork assembly attached to the front portion and pivotable about a steering axis; (3) a front wheel on the fork assembly, the front wheel having a front sprocket; (4) a rear wheel on the rear portion, the rear wheel having a rear sprocket and (5) a drive mechanism that includes a main-drive sprocket at the lower end of the center portion. The improvement comprises a chain-driven front-drive mechanism having a gear arrangement attached to the fork assembly, whereby the gear arrangement transfers rotational power from the drive mechanism along the steering axis to the front sprocket. With the chain-driven front wheel, as with typical bicycle back wheels, a free-wheeling ratcheting may be included.
In a first embodiment of the invention, the gear arrangement of the two-wheel-drive bicycle further includes a fixed-axis intermediate rotatable transfer device that is attached to the front portion of the frame and mechanically engaged to the drive mechanism. A variable-axis intermediate rotatable transfer device is attached to the fork assembly and mechanically engaged to the front sprocket, and a drive-transfer wheel capable of rotation is attached to the fork assembly and engaged between the fixed-axis intermediate and variable-axis intermediate transfer devices in such a manner that the drive-transfer wheel mechanically links the front sprocket with the main-drive sprocket while allowing bicycle steering.
In one version of the first embodiment, the fixed-axis intermediate rotatable transfer device includes a rotary-drive input sprocket and the variable-axis intermediate rotatable transfer device includes a rotary-drive output sprocket. In a particular version of such embodiment, a front chain engages the variable-axis intermediate rotatable transfer device to the front sprocket. Furthermore, a transverse sprocket arrangement is connected to the center portion between the main-drive-sprocket and the top end of the center portion. A first transverse-drive chain engages the transverse sprocket arrangement and extends to the fixed-axis intermediate rotatable transfer device, and a second transverse-drive chain engages the transverse sprocket arrangement and extends to the rear sprockets.
In a still more particular version of the first embodiment, the transverse sprocket arrangement includes a first central-drive sprocket attached to the center portion and a second central-drive sprocket attached to the center portion and coaxially connected to the first central-drive sprocket. Furthermore, the transverse-drive chain includes a first chain extending from the fixed-axis intermediate rotatable transfer device to the first central-drive sprocket and a second chain extending from the second central-drive sprocket to the rear sprocket. In still another version of the embodiment, a clutch is used such that the front-drive mechanism can be disengaged from the main-drive-sprocket.
In still another embodiment of the invention, the fixed-axis intermediate rotatable transfer device rotates about a center axis and the drive-transfer wheel assembly has a center axis perpendicular to the center axis of the fixed-axis intermediate rotatable transfer device. In a particular version of this embodiment, the drive transfer wheel has a center axis, the fixed-axis intermediate rotatable transfer device and the variable-axis intermediate rotatable transfer device each rotate about a center axis, and the axes of the fixed-axis intermediate rotatable transfer device and the variable-axis intermediate rotatable transfer device are substantially perpendicular to the center axis of the drive transfer wheel. In still another version, the fixed-axis intermediate rotatable transfer device is attached to a side of the front portion of the frame opposite the variable-axis intermediate rotatable transfer device.
In a preferred version of the first embodiment, the gear arrangement includes a fixed-axis intermediate sprocket assembly rotatably attached to the front portion and having a first input sprocket mechanically engaged to the drive mechanism and a first output sprocket. A variable-axis intermediate sprocket assembly capable of rotating is attached to the fork assembly and includes a second input sprocket and a second output sprocket mechanically engaged to the front sprocket, and a drive-transfer wheel circumscribing and rotatably attached to the fork assembly and mechanically engaged to the first output sprocket and the second input sprocket, thereby providing front-wheel drive while allowing pivoting of the fork assembly for bicycle steering.
In the most preferred embodiment of the invention, the gear arrangement comprises: (1) a fixed-axis intermediate sprocket assembly rotatably attached to the front portion and having a first input sprocket mechanically engaged to the drive mechanism and a first output sprocket; (2) a first fixed-axis gear wheel attached to the front portion and mechanically engaged to the fixed-axis intermediate sprocket; (3) a second gear wheel engaged with the first fixed-axis gear wheel, the second gear wheel circumscribing the steering axis; (4) a drive shaft oriented along the steering axis, the drive shaft having a first and second end, where the first end is connected to the second gear wheel and the second end is connected to a third gear wheel oriented parallel to the second gear wheel; and (5) a fourth gear wheel engaged with the third gear wheel and mechanically engaged to the front sprocket.
In one version of the most preferred embodiment, the first, second, third and fourth gear wheels are beveled gears.
In still another version of the most preferred embodiment, a transverse-drive chain engages the fixed-axis intermediate sprocket assembly with a transverse sprocket arrangement that is connected to the center portion between the main-drive-sprocket and the top end of the center portion.
In still another version of the most preferred embodiment, the-transverse sprocket arrangement includes a first central-drive sprocket attached to the center portion and a second central-drive sprocket attached to the center portion and coaxially connected to the first central-drive sprocket. In yet another version, the transverse-drive chain includes a first chain extending from the fixed-axis intermediate sprocket assembly to the first central-drive sprocket and a second chain extending from the second central-drive sprocket to the rear sprocket. In still another version, the two-wheel-drive bicycle includes a clutch, whereby the front-drive mechanism can be disengaged from the main-drive sprocket.
In yet another version of the preferred embodiment, a front-drive chain transfers rotational drive from the fourth gear wheel to the front-sprocket wheel.